It's no secret that Friday the 13th took inspiration from early slasher horror movies like Halloween, but it copied most of its elements from one 1970s Italian horror movie. Friday the 13th's screenwriter, Victor Miller, has plainly said that he saw Halloween and wanted to make a similar movie in a new location while also being inspired by teen sex comedies that were popular at the time. The original Friday the 13th, released in 1980, was so successful that it spawned 11 sequels, including a crossover movie with Freddy Krueger.

The American influences on Friday the 13th are clear, as the film takes the basic premise of slasher horror movies like 1978's Halloween and 1974's The Texas Chain Saw Massacre. Both of these involve a group of teens who are stalked by a killer until a "final girl" emerges and defeats the villain or escapes the horror. Friday the 13th put a spin on the genre by being set at a summer camp and having a shocking twist at the end. The most notable addition that it brought to the budding slasher genre was copious amounts of violence and gore, courtesy of Tom Savini's special effects.

Related: Friday The 13th's Deleted Opening Death Scene Urban Myth Explained

The main inspiration for the stalk-and-slash format and the violence of Friday the 13th and its first sequel is attributed not to Halloween or The Texas Chain Saw Massacre, however, but to Mario Bava's 1971 movie A Bay of Blood. Bava's Italian horror classic came out before Friday the 13th's other influences, including the 1974 slasher film pioneer Black Christmas. A Bay of Blood is commonly known as "the grandfather of the modern slasher film," featuring a killer seen in POV stalking and killing young people in a wooded setting in increasingly violent ways.

The Shot-For-Shot A Bay Of Blood Death Scene Homages In Friday The 13th

Betsy Palmer as Pamela Voorhees in Friday the 13th

Friday the 13th and its heavily edited sequel, Friday the 13th Part 2, take so much inspiration from A Bay of Blood that two of their death scenes are nearly identical to kills in Bava's film. The most noticeable comparison is in Friday the 13th Part 2 when a couple in bed gets impaled by a spear simultaneously — a double death lifted from A Bay of Blood nearly shot-for-shot. The original Friday the 13th also features a character getting killed by an ax to the face, mimicking a similar shocking scene in Bava's movie in which a character opens the door to the killer and gets a machete embedded in his face.

While Friday the 13th's American inspirations, like Halloween, are well-documented, the inspiration from Mario Bava's gory proto-slasher movie A Bay of Blood is often overlooked. Italian genre movies of the 1970s, like the popular Spaghetti Westerns, lifted a lot from American cinema stylistically and thematically, but this is a unique inverse of that, as the parallels between the precursor A Bay of Blood and Friday the 13th are very clear.